Dissertations / Theses on the topic 'Magnetometer calibration'

This work addresses the relevant errors of the anisotropic magnetoresistance sensor for inertial navigation systems. The manuscript provides resulting guidelines and solution for using the AMR sensors in a robust and appropriate way relative to the applications. New methods also are proposed to improve the performance and, reduce the power requirements and cost design of the magnetometer. The new compensation method is proposed by developing an optimization algorithm. The necessity of the sensor calibration is shown and the source of the errors and compensating model are investigated. Two novel methods of indoor calibration are proposed and examples of operating systems are presented.

CHAMP (CHAllenging Minisatellite Payload) is a German small satellite mission to study the earth's gravity field, magnetic field and upper atmosphere. Thanks to the good condition of the satellite so far, the planned 5 years mission is extended to year 2009. The satellite provides continuously a large quantity of measurement data for the purpose of Earth study. The measurements of the magnetic field are undertaken by two Fluxgate Magnetometers (vector magnetometer) and one Overhauser Magnetometer (scalar magnetometer) flown on CHAMP. In order to ensure the quality of the data during the whole mission, the calibration of the magnetometers has to be performed routinely in orbit. The scalar magnetometer serves as the magnetic reference and its readings are compared with the readings of the vector magnetometer. The readings of the vector magnetometer are corrected by the parameters that are derived from this comparison, which is called the scalar calibration. In the routine processing, these calibration parameters are updated every 15 days by means of scalar calibration. There are also magnetic effects coming from the satellite which disturb the measurements. Most of them have been characterized during tests before launch. Among them are the remanent magnetization of the spacecraft and fields generated by currents. They are all considered to be constant over the mission life. The 8 years of operation experience allow us to investigate the long-term behaviors of the magnetometers and the satellite systems. According to the investigation, it was found that for example the scale factors of the FGM show obvious long-term changes which can be described by logarithmic functions. The other parameters (offsets and angles between the three components) can be considered constant. If these continuous parameters are applied for the FGM data processing, the disagreement between the OVM and the FGM readings is limited to pm1nT over the whole mission. This demonstrates, the magnetometers on CHAMP exhibit a very good stability. However, the daily correction of the parameter Z component offset of the FGM improves the agreement between the magnetometers markedly. The Z component offset plays a very important role for the data quality. It exhibits a linear relationship with the standard deviation of the disagreement between the OVM and the FGM readings. After Z offset correction, the errors are limited to pm0.5nT (equivalent to a standard deviation of 0.2nT). We improved the corrections of the spacecraft field which are not taken into account in the routine processing. Such disturbance field, e.g. from the power supply system of the satellite, show some systematic errors in the FGM data and are misinterpreted in 9-parameter calibration, which brings false local time related variation of the calibration parameters. These corrections are made by applying a mathematical model to the measured currents. This non-linear model is derived from an inversion technique. If the disturbance field of the satellite body are fully corrected, the standard deviation of scalar error triangle B remains about 0.1nT. Additionally, in order to keep the OVM readings a reliable standard, the imperfect coefficients of the torquer current correction for the OVM are redetermined by solving a minimization problem. The temporal variation of the spacecraft remanent field is investigated. It was found that the average magnetic moment of the magneto-torquers reflects well the moment of the satellite. This allows for a continuous correction of the spacecraft field. The reasons for the possible unknown systemic error are discussed in this thesis. Particularly, both temperature uncertainties and time errors have influence on the FGM data. Based on the results of this thesis the data processing of future magnetic missions can be designed in an improved way. In particular, the upcoming ESA mission Swarm can take advantage of our findings and provide all the auxiliary measurements needed for a proper recovery of the ambient magnetic field.
CHAMP (CHAllenging Minisatellite Payload) ist eine deutsche Kleinsatellitenmission für die Forschung und Anwendung in Bereich der Geowissenschaften und Atmosphärenphysik. Das Projekt wird vom GFZ geleitet. Mit seinen hochgenauen, multifunktionalen, sich ergänzenden Nutzlastelementen (Magnetometer, Akzelerometer, Sternsensor, GPS-Empfänger, Laser-Retroreflektor, Ionendriftmeter) liefert CHAMP erstmalig gleichzeitig hochgenaue Schwere- und Magnetfeldmessungen (seit Mitte 2000). Dank des bisherigen guten Zustandes des Satelliten ist die auf 5 Jahre ausgelegte Mission bis 2009 verlängert geworden. An Board befinden sich ein skalares Overhauser-Magnetometer(OVM) für Kalibrierungszwecke sowie zwei Fluxgate-Magnetometer(FGM) zur Messung des magnetischen Feldvektors. Die Messungen vom FGM werden immer verglichen mit denen vom OVM und korregiert im Fall von Widersprüche, das ist die sog. Skalar-Kalibrierung. Um eine zuverlässige Datenqualität während der 8 jährigen Mission zu garantieren, ist die Nachkalibrierung implementiert. Im Rahmen der standard mäßigen Datenverarbeitung werden die Instrumentenparameter des FGM alle 15 Tage neu bestimmt. Das Ziel der vorliegenden Arbeit ist es, eine Verbesserung der Vektormagnetfelddaten zu erzielen durch eine neue Methode der Kalibrierung, die die Eigenschaften der Sensoren und Störung vom Raumfahrzeug mit berücksichtigt. Die Erfahrung aus den zurückliegenden Jahren hat gezeigt, dass sich die Skalenfaktoren des FGM stark mit der Zeit ändern. Dieser Verlauf lässt sich gut durch eine Logarithmuskurve anpassen. Andere Parameter wie die Winkel und die Offsets scheinen stabil zu sein. Eine Ausnahme macht der Offset der Z-Komponent. Dieser bedarf einer regelmäßigen Korrektur. Während die Standardverarbeitung eine undifferenzierte Bestimmung aller 9 FGM Parameter durch nicht-lineare Inversion der skalar Daten vornimmt, beziehen wir jetzt die langzeitlichen Eigenschaften der Parameter in die Bestimmung mit ein. Eine weitere Verbesserung der CHAMP-Magnetfelddaten konnte erreicht werden durch geeignete Berücksichtigung von Störung vom Raumfahrzeug. Die verbleibenden Unsicherheiten konnten durch diese Maßnahmen auf eine Standardabweichung von 0.1nT reduziert werden.

JUICE is a future ESA mission exploring Jupiter's system and in particular investigating Ganymede's environment. One of the most important instruments of the spacecraft is the magnetometer, which allows to study Ganymede's ocean. The magnetometer needs a precise calibration to provide accurate measurements, thus roll campaigns to determine its offset needs to be done during the mission. This thesis focuses on the analysis of the different versions of the trajectory of JUICE to verify whether the requirements reported in the calibration plan written by ESA are satisfied and to examine the variation of the direction of the magnetic field vector B along a single roll of the spacecraft. The roll campaigns for each trajectory characterized by the lowest variation of the direction of B have been identified as the optimum campaigns. Then they have been compared to determine the best trajectory version to choose concerning the calibration phase along the orbit. A modification of the calibration plan has been proposed in order to decrease significantly the variation of the direction of B: performing non-consecutive rolls. CReMA 3.0 is showed to be the best version both considering a roll rate of 0.05 deg/s and 0.07 deg/s and both executing consecutive and non-consecutive rolls.

In this study the main aim has been to analyse and improve some important aspects of the in-flight calibration process for the three Earth fly-bys planned for the ESA JUICE space mission. In fact it has been developed a calibration script that is capable to correct uncalibrated data from the misallignment and scaling errors towards the expected values of magnetic field from IGRF13 model. Also the experimental process of reproduction of the magnetic field data from JUICE Earth fly-bys prooved the efficiency of the script to control the instrumentation for the gain control during the in-flight calibration. It has also been proved the low influece of the Soft Iron effect on the intrumentation, helping then to reduce the errors associated to misallignments and to the sensors offsets.

Small satellites, and CubeSats in particular, have quickly become a hot topic in the aerospace industry. Attitude determination is currently one of the most intense areas of development for these miniaturized systems and future Cal Poly satellite missions will depend heavily on magnetometers. In order to utilize magnetometers as a viable source of attitude knowledge, precise calibration is required to ensure the greatest accuracy achievable. This paper outlines a procedure for calibrating and testing magnetometers on the next generation of Cal Poly CubeSates, utilizing a Helmholtz cage to simulate any desired orbital magnetic field that would be experienced by a spacecraft around Earth, as well as investigation of magnetic interference as a result of on-board electrical activity.

Experimental testing of attitude determination systems still plays an important role, despite increasing use of simulations. Testing provides a means to numerically quantify system performance, give confidence in the models and methods, and also discover and compensate for unexpected behaviours and interactions with the attitude determination system. The usefulness of the test results is dependent on an understanding of the uncertainties that contribute to the attitude error. With this understanding, the significance of the results can be assessed, and efforts to reduce attitude errors can be directed appropriately. The work of this thesis is to gain a quantitative understanding of the uncertainties that impact the attitude error of low cost spinning spacecraft using COTS camera (as Sun sensor) and MEMS magnetometer. The sensors were calibrated and the uncertainties in these calibrations were quantified, then propagated through the Triad method to uncertainties in the attitude. It was found that most systematic errors were reduced to negligible levels, except those due to timing latencies. Attitude errors achieved in the laboratory with the experimental setup were around 0.14 degrees (3σ) using either the Triad, q-method or Extended Kalman Filter with a gyro for dynamic model replacement. The errors in laboratory were dominated by magnetometer noise. Furthermore, correlated systematic errors had the effect of reducing the attitude error calculated in the laboratory. For an equivalent Sun-mag geometry in orbit, simulation showed that total attitude error would be of the order of 0.77 degrees (3σ). An uncertainty contribution analysis revealed this error was dominated by uncertainties in the inertial magnetic field model. Uncertainties in knowledge of the inertial Sun model, sensor calibration, sensor alignment and sensor noise were shown to be insignificant in comparison.

For synthetic aperture imaging, position and orientation deviation is of great concern. Unknown motions of a Synthetic Aperture Sonar (SAS) can blur the reconstructed images and degrade image quality considerably. Considering the high sensitivity of synthetic aperture imaging technique to sonar deviation, this research aims at providing a thorough navigation solution for a free-towed synthetic aperture sonar (SAS) comprising aspects from the design and construction of the navigation card through to data postprocessing to produce position, velocity, and attitude information of the sonar. The sensor configuration of the designed navigation card is low-cost Micro-Electro-Mechanical-Systems (MEMS) Magnetic, Angular Rate, and Gravity (MARG) sensors including three angular rate gyroscopes, three dual-axial accelerometers, and a triaxial magnetic hybrid. These MARG sensors are mounted orthogonally on a standard 180mm Eurocard PCB to monitor the motions of the sonar in six degrees of freedom. Sensor calibration algorithms are presented for each individual sensor according to its characteristics to precisely determine sensor parameters. The nonlinear least square method and two-step estimator are particularly used for the calibration of accelerometers and magnetometers. A quaternion-based extended Kalman filter is developed based on a total state space model to fuse the calibrated navigation data. In the model, the frame transformations are described using quaternions instead of other attitude representations. The simulations and experimental results are demonstrated in this thesis to verify the capability of the sensor fusion strategy.

Cette thèse aborde le problème de la calibration d’un ensemble de capteurscomposé d’une centrale inertielle, d’un magnétomètre et d’une caméra, avecpour objectif leur intégration sur un système très compact : un mini-drone.Cette étude expose tout d’abord les contraintes imposées par l’application surle choix des capteurs et les solutions envisagées notamment pour résoudre leproblème de la synchronisation des mesures. Après avoir étudié les techniquesde calibration existantes, une méthode permettant la calibration de l’ensembledes capteurs (accéléromètre, gyromètre, magnétomètre et caméra) est présentée.La solution proposée permet également d’estimer les changements de repèresentre les différents capteurs. Elle a la particularité de ne nécessiter l’emploid’aucun matériel particulier. D’autre part, l’intégration de ces capteurs dans unsystème aussi compact soulève de nouvelles difficultés. Dans ces conditions, leschamps magnétiques créés par les actionneurs du drone perturbent les mesuresdu magnétomètre se trouvant à proximité. Une nouvelle méthode est proposéeafin d’estimer et de compenser dynamiquement ces perturbations magnétiquesen fonction de l’état des actionneurs du drone. Enfin, deux applications dusystème comprenant une centrale inertielle et une caméra sont présentées :la construction de mosaïques d’images géo-référencées et la stabilisation devidéos. Ces deux applications exploitent les mesures des capteurs inertiels afind’effectuer un traitement en temps réel pour un coût calculatoire très faible
This thesis deal with the issue of the calibration of a group of sensor composedof an inertial unit, a magnetometer and a camera. It aims at integratingthem into a very compact system : a mini-drone. First of all, this study outlinesthe constraints imposed by the application on the choice of the sensors andthe solutions considered to solve the measures synchronization issue. Afterstudying existing calibration techniques, a method for the calibration of allthe sensors (accelerometer, gyroscope, magnetometer and camera) is presented.The proposed solution allows to estimate the frame transformation between thedifferent sensors. It has the advantage of not requiring the use of any specialequipment. Furthermore, the integration of these sensors into a compact systemraises new difficulties. Under these conditions, the magnetic fields created bythe drone actuators disrupt magnetometer measurements. A new method isproposed to estimate and compensate for these magnetic disturbances. Thecompensation is dynamically adapted based on the state of the drone actuators.Finally, two applications of the system including an inertial unit and a cameraare presented : the construction of geo-referenced images mosaic and videostabilization. Both applications use measurements of inertial sensors and precisecalibration to perform a real-time processing for a very low computational cost

This master's thesis focuses on the utilization of an artificially created weak magnetic field for navigation in 3D space. The theoretical part of this work deals with the general properties of the magnetic field and with its description. The next section of the theoretical part contains an overview of measuring principles for magnetic field measurements. Based on various types of measuring principles, the thesis elaborates on commercially available miniature sensors for magnetic field measurement with a measuring range up to 10 mT. The work focuses mainly on the magnetoresistive principle and fluxgate sensors. Furthermore, the theoretical part contains descriptions of methods for modeling the magnetic field of simple permanent magnets and various magnet assemblies. Lastly, the theoretical part involves a patent search of devices used for locating magnets that are installed in an intramedullary nail, which is used in intramedullary stabilization used on fractures of human bones. By locating the magnet in the nail, it is possible to precisely determine the position of the mounting holes. The practical part of the thesis deals with the analysis of magnetic field behavior in the vicinity of various magnetic assemblies, which were modeled in COMSOL Multiphysics using the finite element method. The models were created with the aim of analysing the behaviour of the magnetic field in the vicinity of the magnets and at the same time to find possible analytical functions that could be used to determine the position of the magnet in space relative to the probe. The result of this work is an analysis of various assemblies, which contains graphs of different dependencies and prescription of polynomial functions that approximate these dependencies. Another part of the thesis is the design of a probe that serves to locate the magnetic target. The work describes two possible methods of localization. For the differential method, a user interface in LabVIEW was created. The probe based on this method is fully capable of locating the magnet in the 2D plane. The state space search method is described only in theory.

Les travaux présentés dans ce mémoire traitent des problèmes relatifs au pilotage et à la localisation d'un robot mobile à roues. Le système de pilotage développé permet d'asservir un véhicule de type fauteuil roulant électrique sur des trajectoires de référence composées de segments rectilignes et de segments en forme de splines polaires. La localisation relative du robot mobile est assurée par un système multicapteur constitué de deux codeurs incrémentaux (odométrie), un gyromètre et un magnétomètre. Le calibrage étant primordial pour les performances du système multicapteur, une méthode d'autocalibrage est développée permettant d'exécuter simultanément et de manière automatique le calibrage de tous les capteurs. La redondance des données sensorielles est exploitée afin d'identifier les paramètres du système qui sont a priori inconnus. L’estimation de l'état du robot mobile est réalisée par un filtre de Kalman étendu développé pour le traitement séquentiel des données sensorielles. Les algorithmes présentés ont été implantés et validés sur la plate-forme expérimentale romane

Microelectromechanical System (MEMS) technology is advancing rapidly. Gyroscopes, accelerometers and magnetometers, also referred to as an Inertial Measurement Unit (IMU), has traditionally been associated with aerospace and industrial robotics but is now within every smart phone. The proliferation of these low-cost devices has facilitated countless new applications with many more still unrealised. This dissertation presents work towards this end. A significant contribution of this work was the development of novel Attitude and Heading Reference System (AHRS) algorithms that fuse together sensor data from an IMU to provide an absolute measurement of orientation relative to the Earth. The novel work presented on non-gyro IMU s demonstrated the potential practical benefits of such kinematically redundant sensor arrays. Low-cost MEMS can only be fully utilised if they are combined with a calibration solution to provide precise measurements with a determined accuracy. This dissertation presents a comprehensive calibration solution to the specific requirements of these sensors based on extensive characterisations investigations. The calibration solutions enable sensors costing <10 United States Dollar (USD) to achieve a static pitch/roll accuracy of <10 and a static heading accuracy of <2°. This performance is equivalent to commercial 1M Us costing up to 3000 USD. The AHRS algorithm and sensor calibration works were brought together in the development of three IMU hardware platforms. To date, >500 have been sold and the open-source associated algorithm downloaded> 10,000 times. Each platform addressed a specific design need and together these facilitated a wide range of new applications; demonstrated by the numerous scientific publications that resulted from collaborative projects and user projects.

The use of a standalone Global Navigation Satellite System (GNSS) has proved to be insufficient when navigating indoors or in urban canyons due to multipath or obstruction. Recent technological advances in low cost micro-electro-mechanical system (MEMS) – based sensors (like accelerometers, gyroscopes and magnetometers) enabled the development of sensor-based navigation systems. Although MEMS sensors are low-cost, lightweight, small size, and have low-power consumption, they have complex error characteristics. Accurate computation of the heading angle (azimuth) is one of the most important aspects of any navigation system. It can be computed either by gyroscopes or magnetometers. Gyroscopes are inertial sensors that can provide the angular rate from which the heading can be calculated, however, their outputs drift with time. Moreover, the accumulated errors due to mathematical integration, performed to obtain the heading angle, lead to large heading errors. On the other hand, magnetometers do not suffer from drift and the calculation of heading does not suffer from error accumulation. They can provide an absolute heading from the magnetic north by sensing the earth’s magnetic field. However, magnetometer readings are usually affected by magnetic fields, other than the earth magnetic field, and by other error sources; therefore magnetometer calibration is required to use magnetometer as a reliable source of heading in navigation applications. In this thesis, a framework for fast magnetometer calibration is proposed. This framework requires little space coverage with no user involvement in the calibration process, and does not need specific movements to be performed. The proposed techniques are capable of performing both 2-dimensional (2D) and 3-dimensional (3D) calibration for magnetometers. They are developed to consider different scenarios suitable for different applications, and can benefit from natural device movements. Some applications involve tethering the magnetometers to the moving platform (like in cars and machinery applications). Other applications are related to portable navigation (smartphone navigation, whether for pedestrians or while driving). The developed framework was examined through experimental work to verify its performance and robustness.
Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2013-05-01 00:52:30.274

碩士
國立交通大學
電控工程研究所
102
Due to error accumulation problem, it is hard to get reliable results of ego-motion estimation by using IMU only. Many methods based on sensor fusion have been proposed to solve this problem. Combining cameras and IMU together is a good choice to get reliable result. By using the information of cameras, the accumulation error from IMU can be constrained. On the other hand, IMU can provide real scale which cameras lack. 　　When cameras pass by the environment where contains similar things, or moves too fast to blur the image, the information from cameras is not robust enough. Therefore, this thesis presents an odometer which combines a magnetometer, monocular camera and IMU to get more reliable results of ego-motion estimation. 　　Because the information from the magnetometer contains the earth's magnetic field and interference, this thesis also presents a magnetometer self-calibration method based on extended kalman filter (EKF). Compared with traditional methods, the proposed method does neither need to pre-calibrate the bias of magnetometer, nor assume the earth's magnetic field vector in reference frame is known. The proposed method is capable of operating even if the disturbance of the earth's magnetic field occurs. Finally, a hardware which integrates with a IMU which has 10 degree of freedom, monocular camera and GPS is used to validate the proposed method in real environment.

碩士
國立成功大學
電機工程學系
106
PHOENIX is a 2U CubeSat in the QB50 project that is designed, assembled, integrated, tested and operated by National Cheng Kung University, Taiwan. After the deployment from International Space Station (ISS) in May 2017, extensive studies on magnetometer calibration have been conducted. The performance of attitude determination and control subsystem (ADCS) for PHOENIX depends on the reliability and accuracy of magnetometer calibration. The thesis is concerned with the in-flight magnetometer calibration which will be naturally influenced by the variation of temperature during the course of orbiting around the earth. A temperature-dependent magnetometer model is proposed and a particle swarm optimization method is adopted in the estimate of calibration parameters. The proposed model and method are verified and tested by using in-flight data from PHOENIX. It has shown that the use of the proposed model together with the optimization method renders a closer match between the magnitudes of the measurement vector and IGRF model. Additionally, the calibration method can be extended to find the suboptimal solution for the satellites with magnetometers without the mechanism of temperature compensation. The proposed approach is believed to be beneficial for small satellites and CubeSats that rely on the use of magnetometer data for attitude determination, orbit determination, and attitude control.